His GC is 10 years period.
It seems he can file extension as early as 6 months before, but I assume if he files now ( Sept. ), his new card will be also expired in Sept. 2024 ( if he still alive to file again ).
Is it count from the exact filing date or the expiration date which is Dec.2014
-He can file I-90 any time from now on even if after the green card expires.
and where to file in Mid West, Missouri?
-Read the following websites:
http://www.uscis.gov/green-card/after-green-card-granted/renew-green-card
http://bbs.wenxuecity.com/immigration/584450.html#postreply